Transcript
iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 1.0 Features ●● Isolated/non-isolated offline 120VAC/230VAC LED driver up to 12W output power ●● Wide line frequency ranges (from 45Hz to 66Hz) ●● Meets IEC61000-3-2 requirement ●● Total harmonic distortion < 15% with PF > 0.95 ●● Wide dimmer compatibility xx Leading-edge dimmer xx Trailing-edge dimmer xx Digital dimmer xx Occupancy sensors and timers ●● Under 20% output ripple current ●● Wide dimming range from 1% to 100% ●● FlickerlessTM LED dimming ●● Resonant control to achieve high efficiency (typical > 85% without dimmer) ●● Over-temperature LED current foldback ●● Small solution size xx Two-stage topology enables small-size input and output filter capacitors xx 200kHz maximum switching frequency enables small transformer xx Intelligent dimmer interface eliminates dedicated high-power bleeder ●● Primary-side sensing eliminates the need for opto-isolator feedback
2.0 Description The iW3616 is a two-stage, high-performance AC/DC offline power supply controller for dimmable LED luminaires. It applies advanced digital control technology to detect the dimmer type and phase, which provides dynamic impedance to interface the dimmer and control the LED brightness at the same time. The iW3616 uses iWatt’s unique digital FlickerlessTM technology to eliminate visible flicker in the entire dimming range and minimize low frequency output ripple current. With advanced dimmer detection technology, the iW3616 can operate with most wall dimmers including leading-edge dimmers (R-type or R-L type) and trailing-edge dimmers (R-C type). In addition, the iW3616’s cycle-by-cycle waveform analysis technology allows fast dimmer setting response. When no dimmer is on the line, the iW3616 optimizes the power factor and minimizes the current harmonic distortion to the AC line. The iW3616 operates the main power converter that delivers constant current to the LED load in quasi-resonant mode to provide high power efficiency and minimize electro-magnetic interference (EMI). It uses iWatt’s patented PrimAccurateTM primary-side sensing technology to achieve excellent LED current regulation under different AC line and LED load voltages, without using a secondary-side feedback circuit and eliminating the need for an opto-coupler. The iW3616 minimizes the external components count by simplifying the EMI filter with iWatt’s EZ-EMI® technology. The intelligent dimmer detection technology eliminates the need for a high-power bleeder. Additionally, the digital control loop of the iW3616 maintains stable overall operating conditions without the need for loop compensation components.
●● Tight LED current regulation (± 5%)
3.0 Applications
●● Fast start-up (< 0.5s without dimmer)
●● Dimmable LED retrofit lamps up to 12W
●● Supports hot-plug LED module (Zhaga)
●● Dimmable LED ballast and luminaries up to 12W
●● Compatible with NEMA SSL6 dimming curve standard ●● Supports wide LED output voltage range ●● Multiple protection features: xx LED open-circuit and short-circuit protection xx Over-current and over-temperature protection xx Current sense resistor short-circuit protection xx AC line over-voltage/-frequency protection
Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers Booster Converter
Flyback Converter
AC Input From Dimmer
VOUT
4 BDRV
1 BVSENSE
3 BISENSE
14 VCB
6
7 VCC FDRV 10
ASU
iW3616
RTN
FISENSE 11 FVSENSE 12
2 VIN
AGND
PGND
CFG
VT
9
8
5
13 NTC
Figure 3.1 : iW3616 Simplified Schematic
Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 4.0 Pinout Description iW3616 VCB 14
1 BV SENSE 2 VIN 3 BISENSE
VT 13 FVSENSE 12
4 BDRV
FISENSE 11
5 CFG
FDRV 10
6 ASU
AGND 9
7 VCC
PGND 8
Pin #
Name
Type
Pin Description
1
BVSENSE
Analog Input
Boost inductor voltage feedback input
2
VIN
Analog Input
Rectified AC line voltage input
3
BISENSE
Analog Input
Boost current sense input
4
BDRV
Output
5
CFG
Analog In/Out
6
ASU
Output
Active start-up and bleeder control
7
VCC
Power
Power supply for control logic and voltage sense for power-on reset circuit
8
PGND
Ground
Power ground
9
AGND
Ground
Signal ground. It should be connected to the power ground on PCB.
10
FDRV
Output
Gate drive output for flyback MOSFET
11
FISENSE
Analog Input
Flyback current sense (used for cycle-by-cycle peak current control and limit)
12
FVSENSE
Analog Input
Flyback voltage sense (used for primary-side regulation and ZVS)
13
VT
Analog Input
External power limit shutdown control and external over-temperature power derating
14
VCB
Analog Input
Boost output voltage feedback input
Base drive output for boost BJT Driver parameter configuration pin and auxiliary driver
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 5.0 Absolute Maximum Ratings Absolute maximum ratings are the parameter values or ranges which can cause permanent damage if exceeded. For maximum safe operating conditions, refer to Electrical Characteristics in Section 6.0.
Parameter
Symbol
Value
Units
DC supply voltage range (pin 7, ICC = 20mA max)
VCC
-0.3 to 18
V
DC supply current at VCC pin
ICC
20
mA
FDRV output (pin 10)
-0.3 to 18
V
BDRV output (pin 4)
-0.3 to 4.0
V
CFG input (pin 5)
-0.3 to 4.0
V
CFG output (pin 5)
-0.3 to 18
V
FVSENSE input (pin 12, I ≤ 10mA)
-0.7 to 4.0
V
BVSENSE input (pin 1, I ≤ 3mA)
-0.7 to 4.0
V
VIN input (pin 2)
-0.3 to 18
V
VCB input (pin 14)
-0.3 to 18
V
FISENSE input (pin 11)
-0.3 to 4.0
V
BISENSE input (pin 3)
-0.3 to 4.0
V
ASU output (pin 6)
-0.3 to 18
V
VT input (pin 13)
-0.3 to 4.0
V
900
mW
TJ MAX
150
°C
Storage temperature
TSTG
-65 to 150
°C
Lead temperature during IR reflow for ≤ 15 seconds
TLEAD
260
°C
ψJB (Note 1)
45
°C/W
ESD rating per JEDEC JESD22-A114
2,000
V
Latch-up test per JEDEC 78
±100
mA
Power dissipation at TA ≤ 25°C Maximum junction temperature
Thermal Resistance Junction-to-PCB Board Surface Temperature
Notes: Note 1. ψJB [Psi Junction to Board] provides an estimation of the die junction temperature relative to the PCB surface temperature. This data is measured at the ground pins (pin 8 and pin 9) without using any thermal adhesives.
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 6.0 Electrical Characteristics VCC = 12 V, -40°C ≤ TA ≤ 85°C, unless otherwise specified (Note 1)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
VIN SECTION Start-up voltage threshold -01
VIN_ST
TA= 25°C, positive edge
0.826
0.918
1.01
V
Start-up voltage threshold -00
VIN_ST
TA= 25°C, positive edge
0.972
1.08
1.188
V
Over-voltage shutdown threshold
VIN_OVP
TA = 25°C, positive edge
1.512
1.68
1.848
V
Input impedance
ZIN
VIN range
VIN
After start-up
5 0
kW 1.8
V
1.98
V
VCB SECTION Over-voltage shutdown threshold
VCB_OVP
Input impedance
ZCB
VCB range
VCB
TA = 25°C, positive edge
1.62
After start-up
1.8 15
0
kW 1.8
V
1
µA
FVSENSE SECTION Input leakage current
IBVS(FVSENSE)
VSENSE = 2V
Normal voltage threshold
VSENSE(NOM)
TA= 25°C, negative edge
1.521
1.536
1.551
V
Output OVP threshold (default)
VSENSE(MAX)
TA= 25°C, negative edge
1.683
1.7
1.717
V
IBVS(BVSENSE)
VSENSE = 0.1V
1
µA
BVSENSE SECTION Input leakage current FDRV SECTION Output low level ON-resistance
RDS_ON_LO(FDRV)
ISINK = 5mA
16
W
Output high level ON-resistance
RDS_ON_HI(FDRV)
ISOURCE = 5mA
25
W
200
kHz
1
W
if VIN_A < 130mV
200
kHz
if VIN_A > 130mV
90
kHz
Maximum switching frequency (Note 2)
fSW_FDRV(MAX)
BDRV SECTION Output low level ON-resistance Maximum switching frequency (Note 2)
RDS_ON_LO(BDRV) fSW_BDRV(MAX)
ISINK = 5mA
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 6.0 Electrical Characteristics (cont.) VCC = 12 V, -40°C ≤ TA ≤ 85°C, unless otherwise specified (Note 1)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
18
V
ASU SECTION Maximum operating voltage
VASU(MAX)
Resistance between VCC and ASU
RVCC_ASU
830
kW
VCC SECTION Maximum operating voltage
VCC(MAX)
Start-up threshold
VCC(ST)
11.5
Under-voltage lockout threshold
VCC(UVL)
6.0
Operating current
17
V
12.5
13.5
V
6.5
7.0
V
ICCQ
6.5
mA
VCC_ASU_OFF
16.25
V
CC regulation threshold limit
VREG_TH(FLYBACK)
1.4
V
ISENSE short protection reference
VRSENSE(FLYBACK)
0.16
V
VOCP(FLYBACK)
1.5
V
Current sink regulation threshold low limit -01 Current sink regulation threshold low limit -00 Current sink regulation threshold high limit -01 Current sink regulation threshold high limit -00
VREG_TH(LO)
0.68
V
VREG_TH(LO)
0.34
V
VREG_TH(HI)
0.92
V
VREG_TH(HI)
0.46
V
ISENSE short protection reference
VRSENSE(BOOST)
0.15
V
VOCP(BOOST)
1.9
V
Power limit high threshold (Note 3)
VP_LIM(HI)
0.56
V
Power limit low threshold (Note 3)
VP_LIM(LO)
0.44
V
Shutdown threshold (Note 3)
VSH_TH
0.22
V
Input leakage current
IBVS(VT)
ASU turn-off threshold FISENSE SECTION
Over-current limit threshold BISENSE SECTION
Over-current limit threshold VT SECTION
VVT = 1.0V
Rev. 0.8 iW3616 Preliminary August 27, 2012
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µA Page 6
iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 6.0 Electrical Characteristics (cont.)
VCC = 12 V, -40°C ≤ TA ≤ 85°C, unless otherwise specified (Note 1)
Parameter Pull-up current source
Symbol
Test Conditions
Min
Typ
Max
Unit
IVT
90
100
110
µA
ICFG
90
100
110
µA
CFG SECTION Pull-up current source Output low level ON-resistance
RDS_ON_LO(CFG)
ISINK = 5mA
30
Ω
Output high level ON-resistance
RDS_ON_HI(CFG)
ISOURCE = 5mA
50
Ω
Notes: Note 1. Adjust VCC above the start-up threshold before setting at 12V. Note 2. Operating frequency varies based on the line and load conditions. See the Theory of Operation section for more details. Note 3. These parameters refer to digital preset values, and they are not 100% tested.
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers
9.0
6.0
VCC Start-up Threshold (V)
VCC Supply Start-up Current (µA)
7.0 Typical Performance Characteristics
TBD
3.0
0.0 0.0
2.0
4.0
8.0 6.0 VCC (V)
10.0
12.0
Internal Reference Voltage (V)
% Deviation of Switching Frequency from Ideal
-0.9 %
-1.5 % -50
-25
0
25
50
75
Ambient Temperature (°C)
100
TBD
11.8
-25
0
25
50
75
Ambient Temperature (°C)
100
125
Figure 7.2 : Start-Up Threshold vs. Temperature
Figure 7.1 : VCC vs. VCC Supply Start-up Current
-0.3 %
12.0
11.6 -50
14.0
0.3 %
12.2
125
Figure 7.3 : % Deviation of Switching Frequency to Ideal Switching Frequency vs. Temperature
Rev. 0.8 iW3616 Preliminary August 27, 2012
2.01
2.00
1.99
1.98 -50
-25
0
25
50
75
Ambient Temperature (°C)
100
125
Figure 7.4 : Internal Reference vs. Temperature
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 8.0 Functional Block Diagram The iW3616 consists of two function blocks: ●● Power factor correction and dimmer interface ●● LED current regulation and dimming control The power factor correction (PFC) and dimmer interfacing block control the boost converter as the first power stage in the iW3616 system (shown in Figure 3.1). It analyzes the rectified AC waveform and determines whether a dimmer is connected on the line. If no dimmer is connected, the block switches the boost BJT (BDRV pin) for PFC and stores the energy in the boost output capacitor. The PFC operation is based on the input voltage (VIN pin), the boost output voltage (VCB pin), and the magnetic flux status of the boost inductor (BVSENSE pin). If a dimmer is connected, the block detects the type of dimmer by analyzing the shape of the rectified AC waveform (VIN pin). It then provides dynamic impedance to interface the dimmer by driving the boost BJT (BDRV pin). The purpose is to match the load requirement of the dimmer VIN
while storing the energy in the boost output capacitor. To provide accurate impedance, the gain (β) of the boost BJT is calibrated (BISENSE pin). The block also measures the dimmer phase conduction angle to determine the dimming level (refer to Section 9.2 for details). The LED current regulation and dimming control block control the flyback or buck/boost converter as the second power stage (shown in Figure 3.1). It switches the flyback MOSFET (FDRV pin) to supply constant current to LED load from the energy stored in the boost output capacitor. The constant current regulation algorithm is based on the information of the transformer primary-side peak current (FISENSE pin) and magnetic flux status of transformer (FVSENSE pin). The block also dims LEDs by adjusting the output current based on dimmer phase conduction angle provided by power factor correction and dimmer interface block. (refer to Section 9.2 for details).
BOCP
VCC
+ –
VCB
+ –
Enable VIN_A VCB_A ZIN
ADC
ZCB ADC MUX
100µA VT CFG
Dimmer Interface and Power Factor Correction Block
BISENSE
1.9V VREG_TH(LO)
+ –
VREG_TH(HI)
Signal Conditioning
Base Driver
BVSENSE
BDRV
10kΩ
100µA MUX
Configuration & Current Foldback
Dimmer Phase
AUX Driver VCC
VCC
Gate Driver
1MΩ ASU
Enable
Start-up Logic
LED Current Regulation and Dimming Control Block
FDRV 65kΩ
Signal Conditioning + –
FOCP
1.5V
FVSENSE FISENSE
+ –
PGND AGND DAC
IPEAK
Figure 8.1 : iW3616 Functional Block Diagram
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 9.0 Theory of Operation 9.1 System Start Up This section provides information about iW3616 system start up, which include the IC startup, wall dimmer detection, and the LED current soft start.
AC line before Walldimmer
9.1.1 IC Startup When AC voltage is applied, the boost output capacitor in (C3 in Figure 11.1) is charged to the peak of line voltage. ASU pin is open by default so that ASU BJT (Q3 in Figure 11.1) is turned on and VCC capacitors (C8 and C9 in Figure 11.1) is charged through ASU resistor (R9 in Figure 11.1) and ASU BJT. When the VCC voltage reaches start-up threshold VCC(ST), the iW3616’s control logic is activated and the IC starts up. The ASU pin is kept open and the ASU circuit continues charging VCC until 50ms after the main flyback converter starts.
AC line after Wall-dimmer
Figure 9.2 : Leading-Edge Wall Dimmer Waveforms
Start-up Sequencing
AC line before Walldimmer
VIN VCC(ST)
VCC
ENABLE
AC line after Wall-dimmer
ASU
Figure 9.3 : Trailing-Edge Wall Dimmer Waveforms Figure 9.1 : Start-up Sequencing Diagram
9.1.2 Wall Dimmer Detection There are two basic categories of phase- cut wall dimmers: leading-edge dimmers and trailing-edge dimmers. If the AC voltage rises at the phase-cut edge, the dimmer is called leading-edge dimmer (shown in Figure 9.2). Otherwise it is called trailing-edge dimmer (shown in Figure 9.3). Normally speaking, leading-edge dimmer is TRIAC based (R-type, RL-type); trailing-edge dimmer is MOSFET or IGBT based (RC-type).
The dimmer detection stage occurs in the iW3616 immediately after IC starts up. The iW3616 is driving the boost BJT (Q2 in Figure 11.1) constantly on to do current sinking during the wall dimmer detection. The purposes of current sinking at startup are: ●● Calibrate the sinking current to 200mA to compensate for the BJT gain variation. This 200mA current sinking is used to latch the leading-edge dimmer during the phase-cut in normal operation. ●● Place a low impedance resistance on the AC line to accurately detect whether a dimmer is connected and the type of dimmer connected. The dimmer type can be determined by looking at the derivative of the input AC voltage. A large positive derivative value indicates a leading-edge dimmer. Otherwise, trailingedge dimmer or no dimmer is detected.
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers Once the dimmer type is determined, the iW3616 needs to qualify the AC input signal before delivering current to the LED load. If under any condition the iW3616 does not see the peak of VIN signal above VIN_ST(MIN) for two consecutive AC half-cycles or the AC line frequency is out of range, the AC input signal is considered as unqualified. The iW3616 will continuously monitor the AC input signal until it sees a qualified AC input signal and then starts to deliver current to the LED load. Or if the VCC drops under VCC(UVL) in this process, the iW3616 will reset and the VCC voltage will charge up again for a fresh start-up. 9.1.3 LED Current Soft-Start After the iW3616 qualifies the AC input signal, the flyback converter will immediately start to deliver constant current to the LED load. A soft-start algorithm is applied to the flyback converter to gradually ramp up the LED current, thus reducing the stress on the LEDs. If no dimmer or a trailingedge dimmer is detected, the output current will ramp up to the target current level within several AC half cycles. If a leading-edge dimmer is detected, the ramp up of the LED current is slower to avoid current over-shoot or undershoot. This is because the leading-edge dimmer’s phase conduction angle is usually not stable when the load on the dimmer is light.
140mV
VCROSS
tCROSS tPERIOD
Figure 9.4 : Dimmer Phase Measurement
And the dimmer phase ratio (D ratio) is calculated as: Dimmer Phase Ratio (D ratio) = tCROSS/tPERIOD
(9.1)
The tPERIOD is the period of AC half cycle, which is measured by the time span between the moments that VIN rises above the 140mV reference in two consecutive AC half cycles. If the D ratio is above 90%, the iW3616 considers no dimmer is on the line. 9.2.2 Dimming Curve
If a dimmer is connected, the boost converter will start immediately into leading-edge or trailing-edge mode operation (refer to Section 9.31 and 9.32 for details) to interface the dimmer. If no dimmer is connected, the boost converter will start PFC operation (refer to Section 9.33 for details).
The iW3616 dims the LED by reducing the output current to a certain percentage of the LED current level when there is no dimmer, which is called dimming percentage. A mapping between the D ratio and the dimming percentage is predetermined in the iW3616. There are two different mapping options, or dimming curves, that can be selected with the CFG pin (refer to Section 9.5 for details). Both dimming curves fall within the limits of the NEMA SSL6 standard (as shown in Figure 10.6). The iW3616 updates the dimming percentage based on the D ratio measurement every AC half cycle to ensure fast dimmer response.
9.2 Phase Measurement and Dimming Curve
9.3 Dimmer Interface and Power Factor Correction Block Operation
This section provides information about iW3616 phase measurement and dimming curve.
This section provides information about iW3616 dimmer interface and power factor correction block’s operation, which includes leading-edge dimmer mode, trailing-edge dimmer mode, no dimmer mode, and transition between these operation modes.
9.2.1 Phase Measurement Dimmer phase conduction angle is measured every AC half cycle. Dimmer phase is determined by the time period that VIN stays above the zero-crossing threshold (tCROSS) as shown in Figure 9.4. The threshold is 140mV.
9.3.1 Leading-Edge Dimmer Mode If a leading-edge dimmer is detected on the line, the boost converter is operated in leading-edge dimmer mode. This mode provides dynamic impedance matching for the leading-edge dimmers. The leading-edge mode operation can be split into five intervals, as shown in Figure 9.5.
Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers
0
1
2
3
4
0 0
1
2 3
0
BJT(drive) BJT(drive) ASU(en) ASU(en)
Figure 9.5 : Leading-Edge Boost Mode Operation
Figure 9.6 : Trailing-Edge Boost Mode Operation
During interval 0, the TRIAC in the leading-edge dimmer is turned off and the dimmer requires a low impedance load to charge its internal timing circuit. The boost BJT (Q2 in Figure 11.1) is driven in current sink mode to provide such low impedance load. When the TRIAC inside the dimmer is fired, the operation enters interval 1. Interval 1 is a short period of time after the TRIAC fires. The boost BJT is kept in current sink mode to provide 200mA latching current for the TRIAC. Then the operation enters interval 2. The boost BJT is in switching mode during interval 2. Interval 2 ends at 90˚ of the phase angle. During Interval 2, the iW3616 boosts the energy into the boost output capacitor and provides the holding current of the TRIAC at the same time. Interval 3 is a 400µs blanking time to ensure the TRIAC turns off after enough energy is boosted into the boost output capacitor. Then the operation enters interval 4 in which the boost BJT is in light duty-cycle switching mode to discharge the EMI filter capacitors of the LED driver.
During interval 0, the boost BJT is driven in current sink mode to reset the dimmer with a low impedance load. Interval 1 begins as the VIN rises above the zero crossing reference. The boost BJT is driven in switching mode to boost energy into the boost output capacitor. Then interval 2 starts at a short period of time before the phase-cut edge to increase the switching duty cycle as a transition state between interval 1 and interval 3. Interval 3 begins right at the phasecut edge. The boost BJT switches with four times of the duty cycle as in interval 1 to quickly discharge the EMI capacitor inside the dimmer so as to ensure the accurate phase.
9.3.2 Trailing-Edge Dimmer Mode
9.3.3 No Dimmer Mode (PFC Operation) If there is no dimmer on the line, boost converter is operated in PFC mode for optimal power factor and minimum harmonic distortion. The iW3616 switches the boost BJT in valley mode switching to minimize the switching loss and EMI. Input current will follow the input voltage as shown in Figure 9.7.
If a trailing-edge dimmer is detected on the line, the boost converter is operated in trailing-edge dimmer mode. This mode provides dynamic impedance matching for trailingedge dimmers. The operation can be split into four intervals, as shown in Figure 9.6.
VAC
Inductor Current Input Current
Figure 9.7 : No Dimmer Boost Mode Operation
The iW3616’s PFC algorithm is based on fixed on-time switching with the compensation of dead-time after the boost inductor resets. The dead-time is measured from the moment that boost inductor resets (determined by BVSENSE Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers pin) to the following boost BJT turn-on moment (determined by BDRV pin). To maximize the power efficiency, the boost output capacitor voltage is set to be 30V above the peak AC line voltage for 230V AC input and 15V above for 120V AC input. 9.3.4 Transition Between Operation Modes The iW3616 constantly monitors the derivative of the VIN signal every AC half cycles to ensure the boost converter’s operation is in the correct mode. The mode of the operation is continuously updated based on the latest detected dimmer type. The iW3616 also monitors dimmer existence by looking at the D ratio. If the D ratio is greater than 90% at any time, the boost converter will enter the No Dimmer mode immediately.
9.4 LED Current Regulation and Dimming Control Block Operation This section provides information about iW3616 LED current regulation and dimming control block operation. 9.4.1 Cycle-by-Cycle LED Current Regulation The LED current regulation and dimming control block incorporates the iWatt-patented PrimAccurateTM technology. Constant current is guaranteed regardless of the input voltage (boost output capacitor voltage) or the output voltage (LED load forward voltage) of the flyback converter. Figure 9.8 shows the basic principle of this constant current regulation algorithm. tOFF
tON
The LED load current can be determined by an equation as shown below. IOUT = 0.5 × NTR × IPK × TR / TP
(9.2)
where IPK is the peak of primary winding current. NTR is the primary-secondary turns ratio. TR is the secondary winding current ramp-down time, or the transformer reset time. TP is the entire switching period. The IPK is determined by the voltage generated on the current-sense resistor: IPK = VPK / RS. Therefore, the equation can be written as: IOUT = 0.5 × NTR / RS × (VPK × TR / TP)
(9.3)
The iW3616 measures TR and TP on a cycle-by-cycle basis and controls VPK so that the KCC = VPK × TR / TP is always a constant. The KCC is an internally defined constant that equals to 0.7V. Therefore, the IOUT can be determined by the turns-ratio and current sense resistor at the design time of the application circuit. 9.4.2 Dimming Control
tS
iW3616 has two dimming scheme options which can be selected by the CFG pin (refer to Section 9.5 for details). The first one is pulse width modulation (PWM) dimming. The second one is constant current pulse frequency modulation (CC-PFM) dimming.
IP
IS
●● PWM Dimming Mode
IO
current ramps up linearly and energy builds up in the transformer. The iW3616 turns off the MOSFET when the primary winding current reaches the peak current regulation level. At this moment, the transformer maintains the magnetic flux so that the energy in the transformer generates the secondary winding current that equals to the peak primary winding current multiplied by primary-secondary turns-ratio. Then the secondary winding current ramps down linearly until all the energy in transformer is discharged. After the energy in the transformer is discharged, the iW3616 starts the next switching cycle. The LED load current is the average of the saw-tooth shaped secondary winding current.
tR Figure 9.8 : Constant Current Regulation
The flyback converter is operated in critical discontinuous conduction mode (CDCM). When the flyback MOSFET (Q1 in Figure 11.1) turns on, the transformer primary winding
From 100% to 25% dimming percentage, the iW3616 employs the same constant current regulation algorithm as described in section 9.4.1 while reducing the KCC constant. As a result, the IOUT will proportionally decrease as the KCC decreases. In this process, the switching frequency of the flyback converter will increase. The maximum switching frequency is clamped at 200kHz. At 25% dimming percentage, the iW3616 will clamp the KCC value and switch to the 630Hz PWM dimming. Further
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers dimming is achieved by only activating the flyback converter during a certain percentage of time in every 630Hz period.
the iW3616 employs an extended discharge time as described below.
●● CC-PFM Dimming Mode
Under the fault condition, the iW3616 tries to start up for three consecutive times. If all three start-up attempts fail, the iW3616 enters the inactive mode, during which the iW3616 does not respond to the VCC power-on requests. The iW3616 is activated again after it sees 29 start-up attempts. The iW3616 can also be reset to the initial condition if the VCC is completely discharged. Typically, this extended discharge time is around three to five seconds, and it allows the iW3616 to support hot-plug LED modules without causing ouput over-voltage while maintaining a quick recovery.
From 100% to 25% dimming percentage, the iW3616 operates in the same KCC-reduction dimming method as described in PWM dimming, except that the frequency clamp changes linearly from 200kHz at 100% dimming percentage to 50kHz at 25% dimming percentage. Below 25% dimming percentage, the iW3616 will switch to the CCPFM mode, which keeps the VPK a constant and increase the TP to achieve further dimming.
9.5 CFG Pin The CFG pin is used to select between the two dimming modes (described in Section 9.42) and the two dimming curves (see Figure 10.6). At startup, the CFG pin outputs ICFG after VCC reaches VCC(ST). The iW3616 reads the CFG pin voltage after 40µs. The dimming curve and dimming mode are selected by connecting a resistor with different values to the CFG pin as shown in Table 9.1 CFG Pin Resistor
Dimming Curve Number (Fig. 10.6)
Dimming Control
CFG Option Number
Value
Tolerance
1
20kW
≤ 5%
1
PWM
2
12.7kW
≤ 5%
1
CC-PFM
3
8.87kW
≤ 5%
2
PWM
4
5.62kW
≤ 5%
2
CC-PFM
Table 9.1 CFG Pin Resistor
9.6 Protection Features This section provides information about iW3616 protection features. 9.6.1 Output Over-Voltage/LED Open Protection The iW3616 includes a function that protects against an output over-voltage.
9.6.2 Output Short Protection The iW3616 includes a function that protects against an output short-circuit fault. If the voltage at the FVSENSE pin is below 0.228V, the iW3616 shuts down immediately. After the shutdown, the iW3616 remains powered, which discharges the VCC. In order to avoid excessive power stress due to auto-restart, the iW3616 employs an extended discharge time (as described in Section 9.61). To support applications with high output capacitance, output short protection is not activated in the initial LED current soft start period. This allows the voltage to build up in the output capacitor without mis-triggering the protection. 9.6.3 Over-Temperature Protection If an NTC thermistor is connected between the VT pin and the GND, the iW3616 is able to detect and protect against an over-temperature event. The iW3616 provides an IVT to the VT pin and detects the voltage on the pin. Based on this voltage, the iW3616 can monitor the resistance of the NTC thermistor, which is related to the temperature of the thermistor. As the VT pin voltage reduces, the iW3616 reduces the power in boost and flyback converter. There is a hysteresis of 84mV on the VT pin voltage for each power limiting step.
The output voltage is monitored by the FVSENSE pin. The ratio between the FVSENSE pin voltage and output voltage is equal to the transformer auxiliary to secondary winding turns-ratio multiplied by the FVSENSE resistor divider ratio (R20, R21 in Figure 11.1). If the voltage at the FVSENSE pin exceeds VSENSE(MAX), the iW3616 shuts down immediately. After the shutdown, the iW3616 remains powered which discharges the VCC. In order to avoid over-charging the output voltage, Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 pulse in the next cycle, and the switching pulse continues if the VOCP(FLYBACK) is not reached; or, the switching pulse turns off again if the VOCP(FLYBACK) is still reached.
100 80
The BISENSE pin provides the same protection mechanism for the boost converter. The BISENSE OCP threshold is VOCP(BOOST) in no dimmer or trailing-edge dimmer mode. The BISENSE OCP threshold is 1.5V in leading-edge dimmer mode.
60 40 20 0.8
1.0
PLI M
(H I)
(L O)
0.6 V
V
0.4 PLI M
0.2
V
0 0.0
SH -T H
Percentage of Nominal Output Current (%)
AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers
VT Pin Voltage
Figure 9.9 : VT Pin Voltage vs. % of Nominal Output Current
When the VT pin voltage reaches VP-LIM(HI) the output current begins to reduce linearly from 100% to 30% as shown in Figure 9.9. At VP-LIM(LO) the output current will be clamped to 1%. If the VT pin voltage further decreases to below VSH_TH, the iW3616 will shut down. The iW3616 will remain in shut-down mode as long as the VT pin voltage is below VSH_TH. If the VT pin voltage rises above VSH_TH at any time, the device will start up and the output will be clamped at 1%. Once the VT pin voltage reaches VP-LIM(LO), the output current will increase to 30%. From VP-LIM(LO) to VP-LIM(HI), the output current will increase linearly from 30% to 100% as shown in Figure 9.9. Finally, the device will go back to normal operation when the VT pin voltage rises above VP-LIM(HI). This bi-directional operation of the VT pin enables the LED current thermal foldback instead of an abrupt shut-down of the light. As the output power decreases under the mild overtemperature condition, the amount of heat generated by the LED also decreases, which reduces the possibility of further temperature rise of the system. When there is a dimmer on the line, the thermal foldback is disabled. The iW3616 will shut down the boost converter and clamp the output current to 1% as soon as the VT pin voltage is below VP-LIM(HI), for safety reasons.
9.6.5 Sense Resistor Short Protection If the FISENSE sense resistor is shorted there is a potential danger of the over-current condition not being detected. Thus the iW3616 is designed to detect this sense-resistor short fault. If the voltage on the FISENSE pin is below VRSENSE(FLYBACK) after 15.6µs of turning on, the sense-resistor short protection is triggered and the iW3616 shuts down immediately. After the shutdown, the VCC is discharged since the iW3616 remains powered. The iW3616 employs an extended discharge time (as described in Section 9.61) before restart. If the BISENSE resistor is shorted, the iW3616 cannot determine the emitter current of the boost BJT, which can ultimately result in the boost BJT exceeding its safe operating area. Thus the iW3616 is designed to detect this boost sense-resistor short fault. When the iW3616 detects a boost-sense-resistor short fault at the detection cycle, the iW3616 shuts down immediately. In the leading-edge and trailing-edge modes, the detection cycle is the zero crossing period in an AC half cycle. If there is no dimmer on the line, the only detection cycle is at start-up. After the shutdown, the VCC is discharged since the iW3616 remains powered. To prevent over-stress on the boost circuit components, the iW3616 employs an extended discharge time (as described in Section 9.61) before restart. 9.6.6 Boost Inductor Short-Protection
9.6.4 Over-Current Protection
The boost inductor is protected from short condition in no dimmer mode. If the BVSENSE pin is not able to see the reset of the boost inductor, the boost inductor short is detected. The iW3616 will short down immediately.
Over-current protection (OCP) is a feature that is built into the iW3616.
9.6.7 AC Input and Boost Output Over-Voltage Protection
With the FISENSE pin the iW3616 is able to monitor the primary peak current of the flyback converter. This allows for cycle-by-cycle peak current control and limit. When the primary peak current multiplied by the FISENSE sense resistor (R15 in Figure 11.1) is greater than VOCP(FLYBACK), over-current is detected and the iW3616 immediately turns off the gate drive until the next cycle. The FDRV pin sends out switching
The iW3616 supports the over-voltage protection of AC input and boost output voltage. If the VIN pin voltage is higher than VIN_OVP for continuous 2ms within every 16ms period, and this condition lasts for eight consecutive AC half cycles, the iW3616 shuts down both the boost and flyback converters. After the shutdown,
Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers the VCC is discharged since the iW3616 remains powered. When VCC drops below below VCC(UVL), the iW3616 resets itself and then initiates a new soft-start cycle. If the VCB pin voltage is higher than VCB_OVP for continuous 128ms, then the iW3616 shuts down both the boost and flyback converters. After the shutdown, the VCC is discharged since the iW3616 remains powered. When VCC drops below VCC(UVL), the iW3616 resets itself and then initiates a new start cycle. Under both the input and boost output over-voltage fault condition, the iW3616 employs an extended discharge time (as described in Section 9.61) before restart.
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 10.0 Performance Characteristics Trailing-Edge Dimmer
Trailing-Edge Dimmer
Time (4.0ms/div)
Time (4.0ms/div)
Figure 10.1 : Trailing-Edge Dimmer
Figure 10.2 : Trailing-Edge Dimmer 2
Leading-Edge Dimmer
Leading-Edge Dimmer
Time (4.0ms/div)
Figure 10.3 : Leading-Edge Dimmer
Time (4.0ms/div)
Figure 10.4 : Leading-Edge Dimmer 2
No Dimmer 100 90 80 70 60 50 40 30 20 10 0 Time (4.0ms/div)
Figure 10.5 : No Dimmer
Rev. 0.8 iW3616 Preliminary August 27, 2012
0
10
20
30
40
50
Dimmer Input Phase (%)
60
70
80
Option 1
90 100 Option 2
Figure 10.6 : Dimming Curve
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 11.0 Typical Application Schematic D11 D1 R1
D3
L3
BR1
N R24
L1
L2 L
R3
R26
+
R9
C4
C3
R11 D7
CX1
+
F1 R2
D5
Q3
C11
D4
+
R30
Q4 R22
C1
iW3616 R5 Q2
C7
R6
7
VCC
PGND
8
6
ASU
AGND
9
5
CFG
FDRV
10
4
BDRV
FISENSE
11
3
BISENSE FVSENSE
12
2
VIN
VT
13
1
BVSENSE
VCB
14
R27
C9
C8
U1 C15
_ D6
Z1 Q1 R12 R14
R13 C10
R18
R19
+
C6
R20
CY1
C5 R15
R21
TH1
Figure 11.1 : iW3616 Typical Application Circuit
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers 12.0 Physical Dimensions 14-Lead SOIC Package D
E
1
H
7
e TOP VIEW
MIN
MAX
MIN
MAX
A
0.053
0.069
1.35
1.75
A1
0.004
0.010
0.10
0.25
B
0.013
0.020
0.33
0.51
C
0.007
0.010
0.19
0.25
D
0.337
0.344
8.55
8.75
E
0.150
0.157
3.80
4.00
e
A1
COPLANARITY 0.10 (0.004)
Symbol
8
14
Inches
A B
SEATING PLANE
α C
0°
SIDE VIEWS
L
Millimeters
0.050 BSC
1.27 BSC
H
0.228
0.244
5.80
6.20
N
0.086 0.118
2.18 3.00
2.39
M
0.094 0.126
L
0.016
0.050
0.40
1.27
α
0°
8°
0°
8°
3.20
Figure 12.1 : Physical dimensions, 8-lead SOIC package Compliant to JEDEC Standard MS12F Controlling dimensions are in inches; millimeter dimensions are for reference only This product is RoHS compliant and Halide free. Soldering Temperature Resistance: [a] Package is IPC/JEDEC Std 020D Moisture Sensitivity Level 1 [b] Package exceeds JEDEC Std No. 22-A111 for Solder Immersion Resistance; package can withstand 10 s immersion < 270˚C Dimension D does not include mold flash, protrusions or gate burrs. Mold flash, protrusions or gate burrs shall not exceed 0.15 mm per end. Dimension E does not include interlead flash or protrusion. Interlead flash or protrusion shall not exceed 0.25 mm per side. The package top may be smaller than the package bottom. Dimensions D and E are determined at the outermost extremes of the plastic bocy exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mismatch between the top and bottom of the plastic body.
13.0 Ordering Information Part Number
Options
Package
Description
iW3616-00
120VAC Input
SOIC-14
Tape & Reel1
iW3616-01
230VAC Input
SOIC-14
Tape & Reel1
Note 1: Tape & Reel packing quantity is 2,500/reel.
Rev. 0.8 iW3616 Preliminary August 27, 2012
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iW3616 AC/DC Digital Power Controller for High Power Factor Dimmable LED Drivers Trademark Information © 2012 iWatt Inc. All rights reserved. iWatt, BroadLED, EZ-EMI, Flickerless, Intelligent AC-DC and LED Power, and PrimAccurate are trademarks of iWatt Inc. All other trademarks and registered trademarks are the property of their respective owners.
Contact Information Web: https://www.iwatt.com E-mail:
[email protected] Phone: +1 (408) 374-4200 Fax: +1 (408) 341-0455 iWatt Inc. 675 Campbell Technology Parkway, Suite 150 Campbell, CA 95008
Disclaimer and Legal Notices iWatt reserves the right to make changes to its products and to discontinue products without notice. The applications information, schematic diagrams, and other reference information included herein is provided as a design aid only and are therefore provided as-is. iWatt makes no warranties with respect to this information and disclaims any implied warranties of merchantability or non-infringement of third-party intellectual property rights. This product is covered by the following patents: 6,385,059; 6,730,039; 6,862,198; 6,900,995; 6,956,750; 6,990,900; 7,443,700; 7,505,287; 7,589,983; 6,972,969; 7,724,547; 7,876,582; 7,880,447; 7,974,109; 8,018,743; 8,049,481; 7,936,132; 7,433,211; 6,944,034. A full list of iWatt patents can be found at www.iwatt.com. Certain applications using semiconductor products may involve potential risks of death, personal injury, or severe property or environmental damage (“Critical Applications”). iWATT SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE‑SUPPORT APPLICATIONS, DEVICES OR SYSTEMS, OR OTHER CRITICAL APPLICATIONS. Inclusion of iWatt products in critical applications is understood to be fully at the risk of the customer. Questions concerning potential risk applications should be directed to iWatt Inc. iWatt semiconductors are typically used in power supplies in which high voltages are present during operation. High-voltage safety precautions should be observed in design and operation to minimize the chance of injury.
Rev. 0.8 iW3616 Preliminary August 27, 2012
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